Comparative study of the fluidity of plasma and disc membranes of bovine rod outer segments by electron-spin resonance

Abstract

The fluidity of isolated plasma and disc membranes from bovine rod outer segments has been compared by electron-spin resonance spectroscopy using the stearic acid spin labels 5-SASL and 16-SASL. This comparison is of interest, given the fact that the disc membranes arise by invagination from the plasma membrane. Analysis of the order parameter in the hydrophilic part of the membrane, and of rotational correlation time in the hydrophobic part, showed a difference of fluidity between these two types of membranes, with a higher fluidity in the disc membranes in both their hydrophilic and hydrophobic regions. For example, at a temperature of 37°C, plasma and disc membranes exhibited values of 0·64 and 0·61 for the order parameter (S), and 9·1 and 14·5s¹ for the rotational correlation frequency (v), respectively. These findings are discussed In relation to previously described differences in the biochemical compositions of the membranes.

Key Words:

• ESR
• membrane fluidity
• ROS
• spin label